Start by baking a butter Lightly pan 9 13-inch. Make the batter as per cookie recipe and fold in 1 cup chopped walnuts along with the chocolate chips batter in prepared pan Spread.. Bake until the edges are light brown and the batter sets, about 45 minutes. Cool slightly and cover surface with 4 cups marshmallows and 1 cup chocolate chips. Broil at least 8 inches from the heat until marshmallows turn golden brown, about 2 minutes. (Keep an eye on the marshmallows, and turn the pan frequently) Cool, cut and serve.